This application is a divisional of application Ser. No. 09/761,218 filed Jan. 16, 2001, now U.S. Pat. No. 6,792,142 the subject matter of which is incorporated by reference herein.
Many different image sensing systems are known in the art.
Viewing of images is limited by the resolution of the viewing screen that is being used. Sometimes, however, the resolution of a view screen is not sufficient to see a specified image, especially one with motion.
For example, a high dynamic range scene may have a dynamic range of 18 bits or even more. This would require a display device that could display 218 resolvable levels of brightness. Many display devices today, however, show only 28=256 levels of brightness.
It is desirable to display an image on such a display while preserving much of its detailed information. Dynamic range compression can be used for this purpose.
It is known to compress dynamic range using logarithmic compression, homomorphic filtering, “cut and paste” methods, and histogram equalization and adjustment. Logarithmic compression carries out a transformation of                     s        =                  255          ⁢          x          ⁢                                          ⁢                                                    log                ⁢                                  (                                      1                    +                                                                g                                                                              )                                            -                              log                ⁡                                  (                                      1                    +                                                                                        G                        ⁢                                                                                                  ⁢                        min                                                                                                    )                                                                                    log                ⁡                                  (                                      1                    +                                                                                        G                        ⁢                                                                                                  ⁢                        max                                                                                                    )                                            -                              log                ⁡                                  (                                      1                    +                                                                                        G                        ⁢                                                                                                  ⁢                        min                                                                                                    )                                                                                        (        5.1        )            
Homomorphic filtering is a frequency domain procedure which associates low frequencies of a Fourier transform of the log of the image with illumination high frequencies. These are associated with reflectance using a filter which associates low-frequency with illumination and high frequency with reflectance.
The cut and paste methods cuts data blocks from different intensity images and pastes them into one background image at corresponding locations. This may produce a gray level which is not a monotonic response to light level, which may produce distortion in the final displayed image.